Struggling for years to find ways of bringing down the nation's stubbornly high figures for ‘karoshi’ - the Japanese term for death by overwork - the government has finally taken drastic measures against some of Japan's biggest employers.

Analysts warn, however, that it may take many years for companies to “culturally implant” new regulations designed to force organisations to honour the law.

In May, the ministry of health, labour and welfare released a list of 334 companies that had been caught repeatedly ignoring labour laws. Some of the firms are among the biggest and most prestigious in Japan, including advertising giant Dentsu Inc, Mitsubishi Electric Corp, Panasonic Corp and Japan Post.

And while that figure may seem high, the ministry ordered no fewer than 6,659 businesses to correct illegal labour practices in the six months from April 2016.

The tactic of naming and shaming organisations with the worst records on employee welfare has been backed by the creation of a Council for the Realisation of Work Style Reform – it held its first meeting in September 2016 – to ensure the terms of the Labour Standards Law are more rigorously enforced.

While the rules on the amount of hours companies can require their employees to put in have been in place for many years, a loophole exists. Under Article 36 of the law, management and labour can sign an agreement that effectively removes all limits.

The benefits for management are obvious, but Japanese employees have also proven easy to convince it is in their best interests to work huge amounts of overtime – often unpaid – to protect the company, their livelihoods and their careers.

Rising numbers of karoshi cases, however, mean that workers are realising the threat overwork poses to their health.

The Japanese government released its first investigation into the karoshi crisis last October, revealing that staff at 12 per cent of organisations put in more than 100 hours of overtime every month.

Employees of a further 23 per cent of the nation's companies are only slightly better off, working 80 hours of overtime each month.

And the true figures may be even worse, as only 1,743 of the 10,000 companies across the nation that were invited to take part in the inquiry did so.

In the 2015 fiscal year, which ended on March 31 2016, the ministry recognised 93 suicides and attempted suicides caused by overwork, enabling dependents to claim compensation. That figure jars with police statistics, however, which indicate that problems related to work were to blame in 2,159 suicides over the course of the same year.

The ministry's figures are also overshadowed by the number of legal cases filed by relatives of victims of karoshi – which are rising fast. In the year to April 2015, 1,456 cases were filed with authorities. By comparison, in the four years between 2004 and 2008, 1,576 cases were filed.

"The government has implemented a number of laws that together are part of a broader reform of working in Japan," said Keith Henry, president of the Tokyo-based Asia Strategy business consultancy.

"The laws on overtime hours have been in place for many years, but a lot of companies simply ignored them," he said.

"And while this is obviously a step in the right direction, I do think it is going to take some years for the rules to be implemented effectively.”